1. Field of the Invention
The present invention relates to a multicolor heat-sensitive recording material, and more particularly relates to a multicolor heat-sensitive recording material comprising a support having disposed thereon at least three heat-sensitive recording layers.
2. Description of the Related Art
Heat-sensitive recording has developed in recent years because recording apparatus therefor are simple, reliable, and maintenance-free. Materials using the reaction between an electron-donating colorless dye and an electron-accepting compound, and materials that utilize the reaction between a diazo compound or a diazonium salt (may be referred to below simply as xe2x80x9cdiazo compound or the likexe2x80x9d) and a coupler, are widely known as materials for heat-sensitive recording.
The development of multicolor heat-sensitive recording materials in recent years has also been remarkable. Such multicolor heat-sensitive recording materials comprise a support having disposed thereon a yellow-forming layer, a magenta-forming layer, and a cyan-forming layer. A multicolor image is formed thereon by heating the respective layers imagewisely.
Multicolor heat-sensitive recording materials typically employ a combination of a color-forming layer (heat-sensitive recording layer) that comprises an electron-donating colorless dye and an electron-accepting compound and a color-forming layer that comprises a diazo compound or the like and a coupler. Generally, the support is successively disposed with the yellow-forming layer, the magenta-forming layer, and the cyan-forming layer.
Image stability inmulticolor heat-sensitive recording materials can be enhanced by utilizing photodecomposition of the diazo compound or the like to irradiate the entire surface of the heat-sensitive recording material after an image has been formed and thereby fix the image. In order to effectively photofix the image, the lowermost layer (i.e., the layer closest to the support) is often a cyan-forming layer comprising an electron-donating colorless dye and an electron-accepting compound. However, there has been a demand for further improvement of image stability with respect to such photofixable heat-sensitive recording materials.
Another large issue has been to enhance color formability. However, multicolor heat-sensitive recording materials that utilize the reaction between an electron-donating colorless dye and an electron-accepting compound are problematic in terms of image stability because the reaction is an equalizing reaction. Further, because the content of the electron-accepting compound must be higher than that of the electron-donating colorless dye, the color-forming layer that contains the electron-donating colorless dye becomes thicker in comparison with the color-forming layer that contains the diazo compound or the like. A thicker color-forming layer results in a thicker multicolor heat-sensitive recording material, which adversely affects color formability.
There is also a problem with conventional multicolor heat-sensitive recording materials in that, when the upper layers are opaque, fixing light is not effectively utilized and fixation takes longer. Additionally, when the upper layers are opaque, the hues of the color-forming layers become turbid and color reproduction regions shrink.
There is another problem in that whiteness cannot be sufficiently enhanced even if a fluorescent brightener is added.
When conventional multicolor recording materials are used as materials for overhead projectors, there is also a problem in that the background is undesirably colored.
In view of the problems described above, an object of the present invention is to provide a multicolor recording material that exhibits high sensitivity during fixation, excellent whiteness, and good hues.
Another object of the invention is to provide a multicolor recording material that has high transparency and is suitable for use with overhead projectors.
A first aspect of the invention provides a multicolor heat-sensitive recording material comprising a support having disposed thereon at least a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer, and a magenta-forming heat-sensitive recording layer, wherein when any one of the heat-sensitive recording layers is disposed on a transparent support and a protective layer is disposed on the any one of the heat-sensitive recording layers, a haze value of the resultant laminate is no greater than 40.
A second aspect of the invention provides a multicolor heat-sensitive recording material comprising a transparent support having disposed thereon a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer, a magenta-forming heat-sensitive recording layer, and a protective layer, wherein the haze value of the recording material is no greater than 50.
According to the first embodiment, the multicolor heat-sensitive recording material of the invention at least has a support having disposed thereon at least a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer, and a magenta-forming heat-sensitive recording layer, and when any one of the heat-sensitive recording layers is disposed on a transparent support and a protective layer is disposed on the any one of the heat-sensitive recording layers, a haze value of the resultant laminate is no greater than 40.
According to this embodiment of the multicolor heat-sensitive recording material, when a laminate is made by sandwiching any one of a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer and a magenta-forming heat-sensitive recording layer between a transparent support and a protective layer, the haze value of the laminate is no greater than 40. In other words, the heat sensitive recording layers which are designed such that, when a laminate is made by sandwiching any one of the heat-sensitive recording layers between a transparent support and a protective layer, the haze value of the laminate is not greater than 40 are laminated on a support. Because of this construction, the transparency of the heat-sensitive layers becomes higher and the fixing light can be effectively utilized. As a result, the fixing speed is raised. In addition, since every heat-sensitive layer has a high transparency, the color of the recording material does not look turbid.
The multicolor heat-sensitive recording material according to this embodiment may further has an intermediate layer and a light transmittance-adjusting layer. Also in the case where an intermediate layer and a light transmittance-adjusting layer are provided, it is preferable that the haze value of the material produced by laminating, on a transparent support, the intermediate layer or the light transmittance-adjusting layer and a protective layer in that order is no greater than 40. The details of the intermediate layer and the light transmittance-adjusting layer are described later.
The haze value as used herein means the value in percentage (%) obtained by dividing the diffuse transmittance by the total light transmittance (i.e., diffuse transmittance÷total light transmittancexc3x97100). The smaller the haze value is, the better the transparency is.
As stated above, if a laminate is made by sandwiching any of the heat-sensitive recording layers between a transparent support and a protective layer, the haze value of the laminate is no greater than 40. This value is preferably no greater than 35 and more preferably no greater than 30. If the haze value exceeds 40, the transparency is lowered and the objective of the invention cannot be achieved.
Examples of the transparent support include synthetic polymer films such as polyester films, e.g., polyethylene terephthalate and polybutylene terephthalate; cellulose triacetate films; and polyolefin films, e.g., polypropylene and polyethylene. These films may be used alone or as laminates thereof.
The thickness of the synthetic polymer film is preferably 25 to 250 xcexcm and more preferably 50 to 200 xcexcm.
The haze value of the transparent support itself is preferably not greater than 10.
If necessary, the protective layer may be made by laminating two or more layers. Examples of the material to be used in the protective layer include water-soluble polymeric compounds such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, vinyl acetate/acrylamide copolymers, silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, gum arabic, casein, hydrolyzates of styrene/maleic acid copolymers, hydrolyzates of styrene/maleic acid copolymer half esters, hydrolyzates of isobutylene/maleic anhydride copolymers, polyacrylamide derivatives, polyvinyl pyrrolidone, sodium polystyrenesulfonate, and sodium alginate; and latices such as styrene/butadiene rubber latex, acrylonitrile/butadiene rubber latex, methyl acrylate/butadiene rubber latex, and vinyl acetate emulsion.
Storage stability can be further improved by crosslinking the water-soluble polymeric compounds. The crosslinking agents can be selected from conventionally known crosslinking agents. Examples of the crosslinking agents include N-methylol urea, N-methylol melamine, and water-soluble initial-stage condensation products such as urea/formalin; dialdehyde compounds such as glyoxal and glutaraldehyde; inorganic crosslinking agents such as boric acid and borax; and polyamide epichlorohydrin.
In addition, a conventionally known pigment, a metal soap, a waxe, a surfactant, and the like may be used in the protective layer.
The coating weight of the protective layer is preferably 0.2 to 5 g/m2, and more preferably 0.5 to 2 g/m2. The thickness is preferably 0.2 to 5 xcexcm and more preferably 0.5 to 2 xcexcm.
When a protective layer is provided, a conventionally known ultraviolet light absorbent or a precursor thereof may be incorporated in the protective layer.
The protective layer can be formed by a conventionally known coating method as in the case where a light-sensitive, heat-sensitive recording layer is formed on a support.
Examples of the support that can be used in this embodiment include plastic films, paper, plastic resin-laminated paper, synthetic paper, etc.
According to the second embodiment, the multicolor heat-sensitive recording material of the invention has a transparent support having disposed thereon a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer, a magenta-forming heat-sensitive recording layer, and a protective layer, and the haze value of the multicolor heat-sensitive recording material is no greater than 50. Accordingly, the multicolor heat-sensitive recording material of the embodiment can be advantageously used in such applications as over head projectors sheets and color slides.
In the multicolor heat-sensitive recording material of this embodiment, although the haze value of the recording material is no greater than 50, the haze value is preferably no greater than 45 and more preferably no greater than 40. If the haze value exceeds 50, the transparency is so reduced that the use as an overhead projector material is difficult.
The transparent support and the protective layer in this embodiment of the multicolor heat-sensitive recording material are the same as those previously described in the first embodiment.
In any of the embodiments described above, it is preferable that each of the heat-sensitive recording layers contains a diazo compound and/or a diazonium salt and a coupler compound which reacts with the diazo compound and/or the diazonium salt to form the respective colors.
In any of the embodiments described above, a light transmittance-adjusting layer and an intermediate layer may be provided.
The light transmittance-adjusting layer contains a component functioning as an ultraviolet light absorbent precursor which does not function as an ultraviolet light absorbent before the irradiation with light having wavelengths in the region required for fixation. For this reason, the light transmittance-adjusting layer has a high light transmittance and sufficiently transmits the light having wavelengths in the region required for fixation. In addition, the light transmittance-adjusting layer has a high transmittance of visible light. Accordingly, the light transmittance-adjusting layer does not hinder the fixation of the heat-sensitive layers. The characteristics of the light transmittance-adjusting layer can be selected in accordance with the characteristics of the photofixable heat-sensitive recording layers.
The ultraviolet light absorbent precursor functions as an ultraviolet light absorbent as a result of reaction caused by light or heat after the irradiation with light having wavelengths in the region required for fixation of the photofixable heat-sensitive recording layer. Accordingly, since most of the light having wavelengths in the ultraviolet region and required for fixation is absorbed by the ultraviolet light absorbent and the transmittance of the ultraviolet lay drops, the lightfastness of the heat-sensitive recording material is improved. But, since the ultraviolet light absorbent does not absorb visible light, the transmittance of visible light does not change substantially.
In the invention, a compound described, for example, in Japanese Patent Application Laid-Open (JP-A) No. 9-1928 can be used as the compound to be incorporated in the light transmittance-adjusting layer.
It is preferable that at least one light transmittance-adjusting layer is provided in the photofixable heat-sensitive recording material. It is most preferable that the light transmittance-adjusting layer is formed between a photofixable magenta heat-sensitive recording layer and, as the outer most layer, the protective layer.
An intermediate layer is provided for the prevention of color mixing between the light-sensitive, heat-sensitive recording layers. It is preferable that the intermediate layer comprises a water-soluble polymeric compound such as gelatin, phthalated gelatin, polyvinyl alcohol, or polyvinyl pyrrolidone. If necessary, the intermediate layer may contain various additives.
When a material, which has a high O2 transmittance, such as laminated paper is used as a support, the lightfastness can be improved by providing a primer layer as an O2 barrier layer.
In order to improve the color mixing-preventive performance and lightfastness by a smaller thickness of the intermediate layer or primer layer, it is effective to incorporate the swellable inorganic laminar compound described in the Japanese Patent Application No. 7-113825 into the intermediate layer or primer layer.
Next, a preferred layer construction of the multicolor heat-sensitive recording material of the invention is explained below. Preferably, the multicolor heat-sensitive recording material of the invention comprises a yellow-forming heat-sensitive recording layer, a cyan-forming heat-sensitive recording layer, and a magenta-forming heat-sensitive recording layer on a support in that order. Preferably, the color-forming layers include a diazo compound or the like and a coupler. More specifically, for example, a preferred construction comprises, a heat-sensitive recording layer containing a diazo compound or the like whose maximum absorption wavelength is 350 nm or less and a coupler capable of reacting with the diazo compound or the like to form a yellow color, a photofixable heat-sensitive recording layer containing a diazo compound or the like whose maximum absorption wavelength is 370xc2x130 nm and a coupler capable of reacting with the diazo compound or the like to form a cyan color, and a photofixable heat-sensitive recording layer containing a diazo compound or the like whose maximum absorption wavelength is 430xc2x130 nm and a coupler capable of reacting with the diazo compound or the like to form a magenta color on a support in that order. In the construction described above, although the yellow-forming heat-sensitive recording layer may be of a non-fixation type, the yellow-forming heat-sensitive recording layer may be of a photofixable heat-sensitive recording layer so as to further enhance the image stability.
In the heat-sensitive recording material of the invention, it is preferable to provide a light transmittance-adjusting layer and an outermost protective layer on a heat-sensitive layer, particularly on a magenta heat-sensitive recording layer. In particular, it is preferable to provide a light transmittance-adjusting layer, whose transmittance to the light having wavelengths within the region to be used for light-fixation diminishes after fixation, between a photofixable magenta heat-sensitive recording layer and a protective layer. In the case of such a heat-sensitive recording material, it is preferable that the light transmittance after the fixation and irradiation with light is not greater than 10% at 350 nm. In this case, the irradiation with light means the irradiation with light of 13 kJ/m2 at a wavelength of 420 nm by means of a xenon-lamp forced radiation tester. More specifically, the irradiation with light means the irradiation with light of 0.9W/m2 for 4.0 hours by means of Weather-Ometer Ci65 (manufactured by Atlas Electric Co.).
The color-forming components, which comprise a diazo compound or the like and a coupler and are incorporated in the heat-sensitive recording layers, may be conventionally known ones. In addition, the heat-sensitive recording materials may contain a basic substance for the acceleration of the reaction between the diazo compound or the like and the coupler, a sensitizer, etc. As described above, combinations of conventionally known diazo compounds or the like and couplers may be used in the heat-sensitive recording material of the invention. But, in order to fully exhibit the effect of the invention, combinations of diazo compounds or the like and couplers, which are suitable for a yellow heat-sensitive layer, a cyan heat-sensitive layer, and a magenta heat-sensitive layer, respectively, exist. These color-forming components and combinations thereof are explained below by way of optimum examples.
Yellow Heat-Sensitive Recording Layer
From the standpoint of effects, the maximum absorption wavelength xcexmax of the diazo compound or the like for use in the yellow heat-sensitive recording layer is preferably 350 nm or less and more preferably 340 nm or less. If the diazo compound or the like has xcexmax on a longer wavelength side relative to the above-mentioned wavelength region, the diazo compound or the like in the yellow heat-sensitive recording layer may be deactivated by the irradiation with light for the fixation of upper layers.
The diazo compound or the like in the yellow heat-sensitive layer to be formed in a position closest to the support is preferably a diazo compound represented by the following general formula (I). 
wherein R1, R2, R3, and R4 each independently represent any one selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, an aryl group, xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51R52, xe2x80x94COR51, xe2x80x94NR51R52, a nitro group, and a cyano group with the proviso that R51 and R52 each independently represent any one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an acyl group; and R5 represents any one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, xe2x80x94COOR53 xe2x80x94CONR53R54, xe2x80x94SO2R53, xe2x80x94SO2NR53R54, and xe2x80x94COR53 with the proviso that R53 and R54 each independently represent any one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an acyl group.
In the general formula (I), R1, R2 , R3, and R4 each independently represent any one selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, an aryl group, xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R52, xe2x80x94SO2NR51R52, xe2x80x94COR51, xe2x80x94NR51R52, a nitro group, and a cyano group.
In the general formula (I), the halogen atoms represented by R1 to R4 are preferably fluorine, chlorine, bromine, and iodine. In particular, fluorine and chlorine are preferable.
In the general formula (I), in the case where R1 to R4 each represents an alkyl group, the alkyl groups include unsubstituted alkyl groups and substituted alkyl groups. Further, the alkyl groups may be straight-chain or branched alkyl groups and may have an unsaturated bond.
In the general formula (I), the examples of the alkyl groups represented by R1 to R4 are preferably alkyl groups having 1 to 20 carbon atoms and more preferably alkyl groups having 1 to 10 carbon atoms. More specifically, preferred examples of the alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, dodecyl, 2-chloroethyl, 2-methanesulfonylethyl, 2-methoxyethyl, 2-benzoyloxyethyl, N,N-dibutylcarbamoylmethyl, 2-ethoxycarbonylethyl, butoxycarbonylmethyl, 2-isopropyloxyethyl, 2-(2,5-di-t-amylphenoxy)ethyl, 2-phenoxyethyl, 1-(4-methoxyphenoxy)-2-propyl, 1-(2,5-di-t-amylphenoxy)-2-propyl, benzyl, xcex1-methylbenzyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethy, etc.
In the general formula (I), in the case where R1 to R4 each represent an aryl group, the aryl groups include unsubstituted aryl groups and substituted aryl groups. The aryl groups represented by R1 to R4 are preferably aryl groups having 6 to 30 carbon atoms. Specifically, preferred examples of the aryl groups include phenyl, 4-methylphenyl, 2-chlorophenyl, etc.
In the general formula (I), in the case where R1 to R4 each represent xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51R52, xe2x80x94COR51, or xe2x80x94NR51R52, R51 and R52 each independently represent any one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an acyl group.
In the general formula (I), the alkyl groups represented by R51 and R52 include unsubstituted alkyl groups and substituted alkyl groups. The alkyl groups represented by R51 and R52 are preferably alkyl groups having 1 to 30 carbon atoms and more preferably alkyl groups having 1 to 10 carbon atoms. Specifically, preferred alkyl groups are methyl, ethyl, isopropyl, sec-butyl, t-butyl, t-amyl, etc.
In the general formula (I), the aryl groups represented by R51 and R52 include unsubstituted aryl groups and substituted aryl groups. The aryl groups represented by R51 and R52 are preferably aryl groups having 6 to 30 carbon atoms. Specifically, preferred aryl groups are phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-chlorophenyl, 2,5-t-amylphenyl, etc.
In the general formula (I), the acyl groups represented by R51 and R52 include unsubstituted acyl groups and substituted acyl groups. The acyl groups represented by R51 and R52 are preferably acyl groups having 1 to 30 carbon atoms and more preferably acyl groups having 1 to 10 carbon atoms. Specifically, preferred acyl groups include acetyl propanoyl, butanoyl, benzoyl, etc.
In the general formula (I), R5 represents any one selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group, an aryl group, xe2x80x94COOR53, xe2x80x94CONR53R54, xe2x80x94SO2R53, xe2x80x94SO2NR53R54, and xe2x80x94COR53.
In the general formula (I), the alkyl groups represented by R5 include unsubstituted alkyl groups and substituted alkyl groups. The alkyl groups may be straight-chain or branched ones and may have an unsaturated bond. The alkyl groups represented by R5 are preferably alkyl groups having 1 to 30 carbon atoms. More specifically, preferred examples of the alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 2-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, dodecyl, 2-chloroethyl, 2-methanesulfonylethyl, 2-methoxyethyl, 2-methoxypropyl, 2-benzoyloxyethyl, N,N-dibutylcarbamoylmethyl, 2-ethoxycarbonylethyl, butoxycarbonylmethyl, octyloxycarbonylmethyl, cyclohexyl, 2-isopropyloxyethyl, 2-(2,5-di-t-amylphenoxy)ethyl, 2-phenoxyethyl, 1-(4-methoxyphenoxy)-2-propyl, 1-(2,5-di-t-amylphenoxy)-2-propyl, benzyl, xcex1-methylbenzyl, phenethyl, 3-phenylpropyl, allyl, methallyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, etc.
In the general formula (I), the aryl groups represented by R5 include unsubstituted aryl groups and substituted aryl groups. The aryl groups represented by R5 are preferably aryl groups having 6 to 30 carbon atoms. Specifically, preferred examples of the aryl groups include phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-isopropylphenyl, etc.
In the general formula (I), in the case where R5 represents xe2x80x94COOR53, xe2x80x94CONR53R54, xe2x80x94SO2R53, xe2x80x94SO2NR53R54, or xe2x80x94COR53, R53 and R54 each independently represent any one selected from the group consisting of a hydrogen atom, an alkyl group, an aryl group, and an acyl group.
In the general formula (I), the alkyl groups represented by R53 and R54 include unsubstituted alkyl groups and substituted alkyl groups. The alkyl groups represented by R53 and R54 are preferably alkyl groups having 1 to 30 carbon atoms and more preferably alkyl groups having 1 to 10 carbon atoms. Specifically, preferred alkyl groups are methyl, ethyl, isopropyl, sec-butyl, t-butyl, t-amyl, etc.
In the general formula (I), the aryl groups represented by R53 and R54 include unsubstituted aryl groups and substituted aryl groups. The aryl groups represented by R53 and R54 are preferably aryl groups having 6 to 30 carbon atoms. Specifically, preferred aryl groups are phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-chlorophenyl, 2,5-t-amylphenyl, etc.
In the general formula (I), the acyl groups represented by R53 and R54 include unsubstituted acyl groups and substituted acyl groups. The acyl groups represented by R53 and R54 are preferably acyl groups having 1 to 30 carbon atoms and more preferably acyl groups having 1 to 10 carbon atoms. Specifically, preferred acyl groups include acetyl, propanoyl, butanoyl, benzoyl, etc.
Specific examples of the diazo compounds represented by the general formula (I) are indicated below by exemplary compounds (A-1 to A-42) and by the specific examples 1 to 28 in which the combinations of R1 to R5 in the general formula (I) are given specifically, but it should be understood that the diazo compounds to be used in the yellow heat-sensitive recording layer are not restricted to these compounds. 
The yellow heat-sensitive recording layer is required to contain at least one kind of the diazo compounds represented by the general formula (I) and may contain two or more kinds of the diazo compounds represented by the general formula (I). Further, other diazo compound may be used together. The content of the diazo compound represented by the general formula (I) in the yellow heat-sensitive recording layer is 0.02 to 3 g/m2 and more preferably 0.1 to 2 g/m2. A content less than 0.02 g/m2 is not desirable in terms of color-formability, and a content more than 3 g/m2 is not desirable in terms of the thickness of the coating layer.
It is preferable that the compound represented by the general formula (I) is used together with an aromatic hydrocarbon. The aromatic hydrocarbon is preferably the one having 12 to 50, preferably 12 to 25 carbon atoms from the standpoints of solubility, ease in handling of the compound in a state to be used, etc. The aromatic hydrocarbons are preferably those represented by the general formula (II): 
wherein R6 to R11 leach independently represent a hydrogen atom or an alkyl group; and n represents an integer of 0 to 3. R6 and R7, R8 and R9, and R10 and R11 may join together, respectively, to form a ring. In the case where R6 to R11 each represent an alkyl group, the alkyl groups may be straight-chain or branched ones and may have an unsaturated bond. Further, the substitution sites of R6 to R9 are not particularly limited.
In the general formula (II), R6 to R9 are preferably a hydrogen atom and alkyl groups having 1 to 8 carbon atoms. R10 and R11 are preferably a hydrogen atom and a methyl group. n is preferably 0 or 1.
The aromatic hydrocarbons are, for example, those given below, but it should be understood that the aromatic hydrocarbons are not restricted to these examples. 
The aromatic hydrocarbons may be used alone or in a combination of two or more thereof.
Next, the coupler which reacts with the above-mentioned diazo compound to form a yellow color is explained below. The coupler that can be used in the yellow heat-sensitive recording layer may be any compound capable of coupling-reacting with a diazo compound to form a dye in a basic environment. All of so-called 4-equivalent couplers known in the field of silver halide photographic light-sensitive materials can be used as couplers in the yellow heat-sensitive recording layer. According to the desired hues of yellow, these couplers can be selected for use.
Examples of conventionally known couplers that can be used in the yellow heat-sensitive recording layer include a so-called active methylene compound having a methylene group adjacent to a carbonyl group, a phenol derivative, and a naphthol derivative. The compounds exemplified below can be used in so far as these compounds meet the purpose of the invention.
Specific examples of the conventionally known couplers include resorcinol, fluoroglycine, sodium 2,3-dihydroxynaphthalene-6-sulfonate, sodium 2-hydroxy-3-naphthalenesulfonate, 2-hydroxy-3-naphthalenesulfonic acid anilide, 1-hydroxy-2-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthalenesulfonic acid morpholinopropylamide, 2-hydroxy-3-naphthalenesulfonic acid-2-ethylhexyloxypropylamide, 2-hydroxy-3-naphthalenesulfonic acid-2-ethylhexylamide, 5-acetamido-1-naphthol, sodium 1-hydroxy-8-acetamidonaphthalene-3,6-disulfonate, 1-hydroxy-8-acetamidonaphthalene-3,6-disulfonic acid dianilide, 1,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2-hydroxy-3-naphthoic acid morpholinopropylamide, 2-hydroxy-3-naphthoic acid octylamide, 2-hydroxy-3-naphthoic acid anilide, 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclopentanedione, 5-(2-n-tetradecyloxyphenyl)-1,3-cyclohexanedione, 5-phenyl-4-methoxycarbonyl-1,3-cyclohexanedione, 5-(2,5-di-n-octyloxyphenyl)-1,3-cyclohexanedione, 1,3-dicyclohexylbarbituric acid, 1,3-di-n-dodecylbarbituric acid, 1-n-octyl-3-n-octadecylbarbituric acid, 1-phenyl-3-(2,5-di-n-octyloxyphenyl)barbituric acid, 1,3-bis(octadecyloxycarbonylmethyl)barbituric acid, 1-phenyl-3-methyl-5-pyrazolone, 1-(2,4,6-trichlorophenyl)-3-anilino-5-pyrazolone, 1-(2,4,6-trichlorophenyl)-3-benzamido-5-pyrazolone, 6-hydroxy-4-methyl-3-cyano-1-(2-ethylhexyl)-2-pyridone, 2-[3-[xcex1-(2,4-di-tert-amylphenoxy)butanamide]benzamide]phenol, 2,4-bis(benzoylacetamino)toluene, 1,3-bis(pivaloylacetaminomethyl)benzene, benzoylacetonitrile, thenoylacetonitrile, acetoacetanilide, benzoylacetanilide, pivalolylacetanilide, 2-chloro-5-(N-n-butylsulfamoyl)-1-pivaloylacetamidobenzene, 1-(2-ethylhexyloxypropyl)-3-cyano-4-methyl-6-hydroxy-1,2-dihydropyridine-2-one, 1-(dodecyloxypropyl)-3-acetyl-4-methyl-6-hydroxy-1,2-dihydropyridine-2-one, 1-(4-n-octyloxyphenyl)-3-tert-butyl-5-aminopyrazole, trifluoroacetoacetanilide, 4-hydroxycoumarin, pyrazolo[1,5-a]pyrimidinedione, 3-ethyl-6-ethoxyuracil, etc.
Details of the couplers are described in, for example, JP-A Nos. 4-201483, 7-125446, 7-96671, 7-223367, 7-22368, etc.
Further, particularly preferred examples of the coupler that can be used in the yellow heat-sensitive recording layer are the compounds represented by the following general formula (III). Details of the couplers represented by the following general formula (III) are described below.
General Formula (III)
E1-CH2-E2
wherein the electron attractive groups indicated by E1 and E2 represent, respectively, a substituent whose Hammett substituent constant "sgr"p is positive. These substituents may be the same or different. Preferred examples of the substituents include acyl groups such as an acetyl group, a propionyl group, a pivaloyl group, a chloroacetyl group, a trifluoroacetyl group, a 1-methylcyclopropylcarbonyl group, a 1-ethylcyclopropylcarbonyl group, a 1-benzylcyclopropylcarbonyl group, a benzoyl group, a 4-methoxybenzoyl group, and a thenoyl group; oxycarbonyl groups such as a methoxycarbonyl group, an ethoxycarbonyl group, a 2-methoxyethoxycarbonyl group, and a 4-methoxyphenoxycarbonyl group; carbamoyl groups such a carbamoyl group, an N,N-dimethylcarbamoyl group, an N,N-diethylcarbamoyl group, an N-phenylcarbamoyl group, an N-2,4-bis(pentyloxy)phenylcarbamoyl group, an N-2,4-bis(octyloxy)phenylcarbamoyl group, and a morpholinocarbonyl group; cyano groups; sulfonyl groups such as a methanesulfonyl group, a benzenesulfonyl group, and a toluenesulfonyl group; phosphono groups such as a diethylphosphono group; and heterocyclic groups such as a benzoxazole-2-yl group, a benzothiazole-2-yl group, a 3,4-dihydroquinazoline-4-one-2-yl group and a 3,4-dihydroquinazoline-4-sulfone-2-yl group.
In the general formula (III), the electron attractive groups indicated by E1 and E2 may join together to form a ring. The rings formed by E1 and E2 are preferably 5- to 6-membered carbocycles or heterocycles.
Specific examples of the coupling components represented by the general formula (III) of the invention are given below, but it should be understood that the invention is not restricted to these examples. 
In the yellow heat-sensitive recording layer, the total amount (mol) of the coupler(s) added is preferably 1 to 10 times, and more preferably 2 to 5 times as large as the amount (mol) of the diazo compound added from the standpoint of the effects.
If the total mol of the coupler(s) added is less than the mol of the diazo compound added, sufficient color-formability may not be obtained. On the other hand, if the total mol of the coupler(s) added is more than 10 times as large as the mol of the diazo compound added, it may impair color-formability and adversely affects the thickness of the layer.
Cyan Heat-Sensitive Recording Layer
In the heat-sensitive recording layer of the invention, the cyan heat-sensitive recording layer is provided between the yellow heat-sensitive recording layer and the magenta heat-sensitive recording layer. From the standpoint of effects, the maximum absorption wavelength xcexmax of the diazo compound or the like for use in the cyan heat-sensitive recording layer is preferably 340 to 400 nm and more preferably 360 to 390 nm. If the diazo compound or the like has xcexmax on a longer wavelength side relative to the above-mentioned wavelength range, the diazo compound or the like may be deactivated by the light irradiation of the upper layer at the time of fixation. On the other hand, if the diazo compound or the like has xcexmax on a shorter wavelength side relative to the above-mentioned wavelength range, image fixability, image preservability, and hue in purple to cyan color formation may be adversely affected depending on the combination with a coupler.
It is preferable that the diazonium salt that can be used in the cyan heat-sensitive recording layer is a compound represented by the following general formula:
Arxe2x80x94N2+.Xxe2x88x92
where Ar represents an aromatic group and Xxe2x88x92 represents an acid anion. The compound undergoes a color forming coupling reaction with a coupler upon heating. Also, the compound is decomposed and deactivated by light. The maximum absorption wavelength of the compound can be controlled by the position and kind of the substituent of the Ar group.
Specific examples of the diazonium that forms the salt include 4-(p-tolylthio)-2,5-dibutoxybenzenediazonium, 4-(4-chlorophenylthio)-2,5-dibutoxybenzenediazonium, 4-(N,N-dimethylamino)benzenediazonium, 4-(N,N-diethylamino)benzenediazonium, 4-(N,N-dipropylamino)benzenediazonium, 4-(N-methyl-N-benzylamino)benzenediazonium, 4-(N,N-dibenzylamino)benzenediazonium, 4-(N-ethyl-N-hydroxyethylamino)benzenediazonium, 4-(N,N-diethylamino)-3-methoxybenzenediazonium, 4-(N,N-dimethylamino)-2-methoxybenzenediazonium, 4-(N-benzoylamino)-2,5-diethoxybenzenediazonium, 4-morpholino-2,5-dibutoxybenzenediazonium, 4-anilinobenzenediazonium, 4-[N-(4-methoxybenzoyl)amino]-2,5-diethoxybenzenediazonium, 4-pyrrolidino-3-ethylbenzenediazonium, 4-[N-(1-methyl-2-(4-methoxyphenoxy)ethyl)-N-hexylamino]-2-hexyloxybenzenediazonium, 4-[N-(2-(4-methoxyphenoxy)ethyl)-N-hexylamino]-2-hexyloxybenzenediazonium, 2-(1-ethylpropyloxy)-4-[di-(di-n-butylaminocarbonylmethyl)amino]benzenediazonium, etc.
Among these diazonium salts, the diazonium salts represented by the following general formula (A), the following general formula (B), and the following general formula (C), respectively, are preferable from the standpoints of hue of dye, image preservability, and image fixability. 
In the general formula (A), Ar represents a substituted or unsubstituted aryl group. R17 and R18 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group and R17 and R18 may be the same or different.
Examples of the substituent include an alkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an acyl group, an alkoxycarbonyl group, a carbamoyl group, a carboamide group, a sulfonyl group, a sulfamoyl group, a sulfonamide group, a ureido group, a halogen atom, an amino group, a heterocyclic group, etc. These substituent groups may be further substituted.
In the general formula (B), R20, R21, and R22 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, with the proviso that R20, R21, and R22 may be the same or different. Y represents a hydrogen atom or an OR19 and R19 represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group.
Examples of the substituents include an alkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an acyl group, an alkoxycarbonyl group, a carbamoyl group, a carboamide group, a sulfonyl group, a sulfamoyl group, a sulfonamide group, a ureido group, a halogen atom, an amino group, a heterocyclic group, etc.
Among these groups, from the standpoint of hue adjustment, Y is preferably a hydrogen atom or an alkyloxy group whose R19 is an alkyl group.
In the general formula (C), R23 and R24 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group. R23 and R24 may be the same or different.
Examples of the substituents include an alkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an acyl group, an alkoxycarbonyl group, a carbamoyl group, a carboamide group, a sulfonyl group, a sulfamoyl group, a sulfonamide group, a ureido group, a halogen atom, an amino group, a heterocyclic group, etc.
In the general formulae (A) to (C), Xxe2x88x92 represents an acid anion. Examples of the acid anion include a polyfluoroalkylcarboxylic acid having 1 to 9 carbon atoms, a polyfluoroalkylsulfonic acid having 1 to 9 carbon atoms, tetrafluoroboron, tetraphenylboron, hexafluorophosphoric acid, an aromatic carboxylic acid, an aromatic sulfonic acid, etc. Hexafluorophosphoric acid is preferable from the standpoint of crystallizability.
Specific examples of the diazonium salts represented by the general formula (A), the general formula (B), and the general formula (C), respectively, are given below. It should be noted, however, that the invention is not limited to these compounds. 
In the invention, the diazonium salts represented by the general formulae (A) to (C) may be used alone or in a combination of two or more. Further, according to purposes such as adjustment of hue, any of the diazonium salts represented by the general formulae (A) to (C) may be used in combination with a conventional diazonium salt.
The content of the diazonium salt in the heat-sensitive recording material of the invention is preferably 0.02 to 3 g/m2, more preferably 0.1 to 2 g/m2, in the heat-sensitive recording layer.
It is preferable that the cyan heat-sensitive recording layer contains as a coupler at least one of the compound represented by the following general formula (D), the compound represented by the following general formula (E), and the compound represented by the following general formula (F). These couplers provide a good cyan hue and a sufficient color density and improve image preservability against light or heat when coupled with a diazonium salt. Other effects to be brought about at the same time include that the color-forming reaction takes place efficiently and thus Dmax is produced by a smaller amount of a diazonium salt and that the fixation sensitivity, stains, etc. can be reduced because the amount of the diazonium salt is reduced. 
In the general formulae (D) to (F), X1, X2, X3, and X4 each independently represent an atomic group required for the formation of a 5-membered aromatic heterocyclic group. Y represents an amino group, a substituted amino group, a hydroxyl group, an alkoxy group, or an alkyl group that may have a substituent. L represents a substituent that can leave at the time of coupling with a diazonium salt. EWG1 and EWG2 each independently represent an electron attractive group. X1 and Y, and EWG1 and EWG2 may join together, respectively, to form a heterocycle.
Among the compounds represented by the general formulae (D) to (F), particularly preferable are the pyrrolopyrimidineone compounds represented by the following general formula (G) and the pyrrolotriazineone compounds represented by the following general formula (H). 
In the general formulae (G) and (H), R7 and R8 each independently represent a hydrogen atom, a halogen atom, an aryl group, an alkyl group, a cyano group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylsulfonyl group, or an arylsulfonyl group. R9 represents an amino group, a substituted amino group, a hydroxyl group, an acyloxy group, an arylcarboxyl group, an alkoxy group, an aryloxy group, an alkylthio group, or an arylthio group. R10 represents a hydrogen atom, a halogen atom, or an electron attractive group whose Hammett substituent constant "sgr"p is 0.2 or more. L represents a substituent that can leave when the compound reacts with a diazonium salt.
Among the substituents represented by R7 and R8, preferably at least one of R7 and R8 is an electron attractive group whose Hammett substituent constant "sgr"p is 0.20 or more. More preferably at least one of R7 and R8 is an electron attractive group whose Hammett substituent constant "sgr"p is 0.35 or more.
Among the electron attractive groups each having a Hammett substituent constant "sgr"p of 0.20 or more, preferred examples of the groups include, but are not limited to, a cyano group (the constant "sgr"p is 0.66), a perfluoroalkyl group (e.g., trifluoromethyl group whose constant "sgr"p is 0.54), an acyl group (e.g., acetyl group whose constant "sgr"p is 0.50 and a benzoyl group whose constant "sgr"p is 0.43), a carbamoyl group (the constant "sgr"p is 0.36), an alkoxycarbonyl group (e.g., ethoxycarbonyl group whose constant "sgr"p is 0.45), etc.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, etc. Among these halogen atoms, a fluorine atom and a chlorine atom are preferable.
In the general formula (G), preferred examples of the electron attractive group represented by R10 whose Hammett substituent constant "sgr"p is 0.2 or more include, but are not limited to, an aryl group, a cyano group, an acyl group, a carbamoyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylsulfonyl group, an arylsulfonyl group, an alkylphosphoryl group, an arylphosphoryl group, a perfluoroalkyl group, etc.
Details of the pyrrolopyrimidineone compounds and the pyrrolotriazineone compounds are described in the specifications of Japanese Patent Application Nos. 11-101546, 11-114929, and 11-317792. All of the compounds described in these specifications can be advantageously used in the invention.
Specific examples of the couplers represented by the general formulae (D) to (F) are given below, but it should be understood that the invention is not restricted to these examples. 
The above-mentioned couplers that can be used in the cyan heat-sensitive recording layer may be used together with a conventionally known coupler according to purposes such as adjustment of hue. Examples of the conventionally known coupler that can be used together include a so-called active methylene compound having a methylene group adjacent to a carbonyl group, a phenol derivative, and a naphthol derivative. The compounds exemplified below can be used in so far as these compounds meet the purpose of the invention. Examples of the conventionally known couplers include the conventionally known couplers exemplified for use in the yellow heat-sensitive recording layer.
In the heat-sensitive recording material of the invention, for the purpose of accelerating the coupling reaction, it is preferable that the heat-sensitive recording layer contains a reducing agent such as aminophenol compounds, phenol compounds, catechol compounds, hydroquinone compounds, amine compounds, hydroxylamine compounds, alcohol compounds, thiol compounds, sulfide compounds, an alkali metal, an alkaline earth metal, a metal hydride, hydrazine compounds, phenidone compounds, aniline compounds, phenylether compounds, an L-ascorbic acid, etc. Among these reducing agents, hydroquinone compounds, catechol compounds, aminophenol compounds are preferable. Specific examples of these reducing agents include, but are not limited to, the exemplary compounds (R-1) to (R-55) described in paragraphs [0067] to [0070] in the specification of Japanese Patent Application No. 2000-116580.
These reducing agents may be dispersed as fine solid particles in the recording layer. The reducing agent may also be used as an emulsion prepared by dissolving the reducing agent alone in an oil. Further, the reducing agent may be added to the oil phase of the emulsion of a coupler. Still further, when the diazo compound or the coupler is enclosed in microcapsules, the reducing agent may be added to the interior of the microcapsules or to both the interior and the exterior of the microcapsules.
The content (mol) of the reducing agent is preferably 1 to 10 times, and more preferably 1 to 4 times as large as the amount (mol) of the diazo compound. When the mol of the reducing agent added is less than that of the diazo compound, color-formability or image preservability may not be sufficiently improved. When the mol of the reducing agent added is more than 10 times the mol of the diazo compounds, the improvement of color-formability may become inconsequential or the preservability of the heat-sensitive recording material may be reduced.
In the cyan heat-sensitive recording layer, the total mol of the coupler(s) added is preferably 0.2 to 8 times, and more preferably 1 to 5 times as large as the mol of the diazonium salt added in the cyan heat-sensitive recording layer from the standpoint of the effects.
When the total mol of the coupler(s) added is less than 0.2 times as large as the mol of the diazonium compound added, sufficient color-formability may not be obtained. On the other hand, when the total mol of the coupler(s) added is more than 8 times, the coatability may deteriorate.
The coupler for use in the invention can be used as a solid-state dispersion prepared by dispersing the coupler together with other components in the presence of a water-soluble polymer in a sand mill or the like. But, it is preferable that the coupler is used as an emulsion prepared by emulsifying the coupler in the presence of a suitable emulsifying aid. The solid-state dispersing method and the emulsifying method are not particularly limited, and methods hitherto known can be employed. The details of these methods are described in JP-A Nos. 59-190886, 2-141279, and 7-17145.
Magenta Heat-Sensitive Recording Layer
The magenta heat-sensitive recording layer is provided as the outermost layer (uppermost layer) of the heat-sensitive recording layers in the heat-sensitive recording material of the invention. From the standpoint of effects, the maximum absorption wavelength xcexmax of the diazo compound or the like for use in the magenta heat-sensitive recording layer is preferably 460 nm or less and more preferably 430 to 460 nm. If the diazo compound or the like has xcexmax on a longer wavelength side relative to the above-mentioned wavelength region, the preservability of the raw heat-sensitive recording material may become inferior. On the other hand, if the diazo compound or the like has xcexmax on a shorter wavelength side relative to the above-mentioned wavelength region, the fixation rate may be reduced. It is preferable that the diazo compound or the like that can be used in the magenta heat-sensitive recording layer is a diazonium salt represented by the following general formula (8): 
wherein R1 and R2 each represent a hydrogen atom, an alkyl group, or an aryl group; R31 represents an alkyl group or an aryl group; and Xxe2x88x92 represents an acid anion.
In the general formula (8), R1, R2, and R31 each represent a hydrogen atom, an alkyl group, or an aryl group; and Xxe2x88x92 represents an acid anion. Since R1 and R2 in the general formula (8) are same as R1 and R2, respectively, in the following general formula (1), R1 and R2 will be described later. The alkyl group represented by R31 in the general formula (8) may have a substituent and is preferably an alkyl group having 1 to 30 carbon atoms. More specifically, preferred examples of the alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, sec-butyl, isobutyl, n-pentyl, 2-pentyl, 3-pentyl, isopentyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, n-dodecyl, cyclohexyl, benzyl, 2-chlorobenzyl, 2-methylbenzyl, 3-chlorobenzyl, 3-methylbenzyl, 3-methoxybenzyl, xcex1-methylbenzyl, allyl, 2-chloroethyl, methoxycarbonylmethyl, methoxycarbonylethyl, and butoxycarbonylethyl. The aryl group represented by R31 may have a substituent and is preferably an aryl group having 6 to 30 total carbon atoms. Specifically, preferred examples of the aryl groups include phenyl, 4-methylphenyl, 3-methylphenyl, 2-methylphenyl, 4-chlorophenyl, and 2-chlorophenyl. It is particularly preferable that the diazonium salt represented by the general formula (8) is a diazonium salt represented by the following general formula (1): 
In the general formula (1), R1 and R2 each independently represent a hydrogen atom, an alkyl group, or an aryl group.
The alkyl group is preferably an alkyl group having 1 to 20 carbon atoms and may be unsubstituted or may have a substituent. More specifically, preferred examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, n-decyl, n-dodecyl, 2-chloroethyl, 2-methanesulfonylethyl, 2-methoxyethyl, N,N-dibutylcarbamoylmethyl, 2-ethoxycarbonylethyl, butoxycarbonylmethyl, 2-isopropyloxyethyl, 2-(2,5-di-t-amylphenoxy)ethyl, 2-phenoxyethyl, 1-(4-methoxyphenoxy)-2-propyl, 1-(2,5-di-t-amylphenoxy)-2-propyl, allyl, benzyl, xcex1-methylbenzyl, 4-chlorobenzyl, 2-chlorobenzyl, 3,4-dichlorobenzyl, 4-fluorobenzyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoromethyl, etc.
The aryl group is preferably an aryl group having 6 to 30 carbon atoms and may be unsubstituted or may have a substituent. Examples of the aryl groups include phenyl, 4-methylphenyl, 2-chlorophenyl, etc.
Among these aryl groups, aryl groups having 6 to 10 carbon atoms are preferable. In particular, a phenyl group and a 4-methylphenyl group are preferable.
In the general formula (1), in the case where both R1 and R2 are alkyl groups, R1 and R2 may join together to form a ring structure that contains a nitrogen. Examples of such cyclic group include a pyrrolidino group, a piperidino group, a morpholino group, a 4-octanoylpiperadino group, a 4-(2-(2,4-di-t-amylphenoxy))butanoylpiperadino group, a 4-(2-(n-octyloxy)-5-t-octylphenyl)sulfonylpiperadino group, a hexamethyleneimino group, an indolino group, etc. Among these groups, a pyrrolidino group and a hexamethyleneimino group are preferable.
It is more preferable that at least one of R1 and R2 in the general formula (1) is a methyl group.
R3 and R4 in the general formula (1) each independently represent a hydrogen atom, an alkyl group, an aryl group, or a halogen atom. The alkyl group and the aryl group have the same meaning as in the case of R1 and R2. It is more preferable that at least one of R3 and R4 in the general formula (1) is a methyl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these halogen atoms, a fluorine atom and a chlorine atom are preferable.
R5, R6, R7, R8, and R9 in the general formula (1) each independently represent a hydrogen atom, an alkyl group, an aryl group, a halogen atom, an alkoxy group, an aryloxy group, an alkoxycarbonyl group, an acyloxy group, a carbamoyl group, an amido group, a cyano group, an alkylthio group, an arylthio group, an alkylsulfonyl group, or an arylsulfonyl group, with the proviso that at least one of R5xcx9cR9 represents a halogen atom.
The alkyl group and the aryl group have the same meaning as in the case of R1 and R2. The halogen atom has the same meaning as in the case of R3 and R4.
The alkoxy group is preferably an alkoxy group having 1 to 20 carbon atoms. The alkoxy group may be unsubstituted or may have a substituent. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-butoxy group, a t-butoxy group, a hexyloxy group, an octyloxy group, a 2-ethylhexyloxy group, a trifluoromethoxy group, a 2-ethoxyethoxy group, a 2-chloroethoxy group, a 2-phenoxyethoxy group, a benzyloxy group, a 2-chlorobenzyloxy group, 4-chlorobenzyloxy group, a 3,4-dichlorobenzyloxy group, an allyloxy-2,4-di-t-amylphenoxyethoxy group, a 2,4-di-t-amylphenoxybutoxy group, etc.
Among these groups, an alkoxy group having 1 to 10 carbon atoms is more preferable. A methoxy group, an ethoxy group, an n-butoxy group, and a benzyloxy group are particularly preferable.
The aryloxy group is preferably an aryloxy group having 6 to 20 carbon atoms. The aryloxy group may be unsubstituted or may have a substituent. Examples of the aryloxy group include a phenoxy group, a 4-methylphenoxy group, a 4-methoxyphenoxy group, a 4-chlorophenoxy group, a 2-chlorophenoxy group, a 2,4-di-t-amylphenoxy group, etc.
Among these groups, an aryloxy group having 6 to 10 carbon atoms is more preferable. A phenoxy group, a 4-methylphenoxy group, and a 4-methoxyphenoxy group are particularly preferable.
The alkoxycarbonyl group is preferably an alkoxycarbonyl group having 2 to 20 carbon atoms. The alkoxycarbonyl group may be unsubstituted or may have a substituent. Examples of the alkoxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group, an n-butoxycarbonyl group, a 2-ethoxyethoxycarbonyl group, etc.
Among these groups, an alkoxycarbonyl group having 2 to 10 carbon atoms is more preferable. A methoxycarbonyl group, an ethoxycarbonyl group, and an n-butoxycarbonyl group are particularly preferable.
The acyloxy group is preferably an acyloxy group having 2 to 20 carbon atoms. The acyloxy group may be unsubstituted or may have a substituent. Examples of the acyloxy group include an acetyloxy group, a butanoyloxy group, a chloroacetyloxy group, a phenoxyacetyloxy group, a benzoyloxy group, etc.
Among these groups, an acyloxy group having 3 to 10 carbon atoms is more preferable. An acetyloxy group, a phenoxyacetyloxy group, and a benzoyloxy group are particularly preferable.
The carbamoyl group is preferably a carbamoyl group having 1 to 20 carbon atoms. The carbamoyl group may be unsubstituted or may have a substituent. Examples of the carbamoyl group include an unsubstituted carbamoyl group, an N,N-dimethylcarbamoyl group, a piperidinocarbonyl group, an N,N-di(2-ethylhexyl)carbamoyl group, etc.
Among these groups, a carbamoyl group having 1 to 10 carbon atoms is more preferable. An unsubstituted carbamoyl group and a piperidinocarbonyl group are particularly preferable.
The amido group is preferably an amido group having 2 to 20 carbon atoms. The amido group may be unsubstituted or may have a substituent. Examples of the amido group include an acetylamino group, a butanoylamino group, a pivaloylamino group, an octanoylamino group, a benzoylamino group, etc.
Among these groups, an amido group having 2 to 10 carbon atoms is more preferable. An acetylamino group and a butanoylamino group are particularly preferable.
The alkylthio group is preferably an alkylthio group having 1 to 20 carbon atoms. The alkylthio group may be unsubstituted or may have a substituent. Examples of the alkylthio group include a methylthio group, an ethylthio group, a butylthio group, an octylthio group, a 2-ethylhexylthio group, a dodecylthio group, a benzylthio group, etc.
Among these groups, an alkylthio group having 1 to 10 carbon atoms is more preferable. A methylthio group, an ethylthio group, a butylthio group, and a benzylthio group are particularly preferable.
The arylthio group is preferably an arylthio group having 6 to 20 carbon atoms. The arylthio group may be unsubstituted or may have a substituent. Examples of the arylthio group include a phenylthio group, 4-chlorophenylthio group, a 2-chlorophenylthio group, and a 4-methylthio group, etc.
Among these groups, an arylthio group having 6 to 10 carbon atoms is more preferable. A phenylthio group and a 2-chlorophenylthio group are particularly preferable.
The alkylsulfonyl group is preferably an alkylsulfonyl group having 1 to 20 carbon atoms. The alkylsulfonyl group may be unsubstituted or may have a substituent. Examples of the alkylsulfonyl group include a methylsulfonyl group, an ethylsulfonyl group, a butylsulfonyl group, an octylsulfonyl group, a dodecylsulfonyl group, a benzylsulfonyl group, etc.
Among these groups, an alkylsulfonyl group having 1 to 10 carbon atoms is more preferable. A methylsulfonyl group, an ethylsulfonyl group, a butylsulfonyl group, and a benzylsulfonyl group are particularly preferable.
The arylsulfonyl group is preferably an arylsulfonyl group having 6 to 20 carbon atoms. The arylsulfonyl group may be unsubstituted or may have a substituent. Examples of the arylsulfonyl group include a phenylsulfonyl group, a 4-chlorophenylsulfonyl group, a 2-chlorophenylsulfonyl group, a 4-methylsulfonyl group, etc.
Among these groups, an arylsulfonyl group having 6 to 10 carbon atoms is more preferable. A phenylsulfonyl group and a 2-chlorophenylsulfonyl group are particularly preferable.
In the general formula (1), in the case where the groups represented by R1 to R9 have substituents, the substituents may each be any one of the diazonium salt represented by the general formula (1) or by the general formula (2) or (6) that will be described later. That is, a dimer of diazonium salts or a polymer having units more than the dimer may be formed.
In the general formula (1), Xxe2x88x92 represents ananion. The anion may be an inorganic anion or an organic anion.
Preferred examples of the inorganic anion include a hexafluorophosphate ion, a borofluoride ion, a chloride ion, a sulfate ion, and a hydrogensulfate ion. Among these anions, a hexafluorophosphate ion and a borofluoride ion are preferable.
Preferred examples of the organic anion include a polyfluoroalkylsulfonate ion, a polyfluoroalkylcarboxylate ion, a tetraphenylborate ion, an aromatic carboxylate ion, and an aromatic sulfonate ion. Among these anions, a polyfluoroalkylsulfonate ion is more preferable.
Among the diazonium salts represented by the general formula (1), a diazonium salt represented by the following general formula (2) is preferable. 
In the general formula (2), R11 and R12 each independently represent an alkyl group. The alkyl group has the same meaning as in the case of R1 and R2 in the general formula (1). R13 and R14 each independently represent a hydrogen atom, an alkyl group, or a halogen atom, and the alkyl group has the same meaning as in the case of R1 and R2 and the halogen atom has the same meaning as in the case of R3 and R4 in the general formula (1). Xxe2x88x92 represents an anion and has the same meaning as in the general formula (1). It is preferable that at least one of R11 and R12 and at least one of R13 and R14 are, respectively, a methyl group.
Ar in the general formula (2) represents the following general formula (3), (4), or (5). 
R16, R17, and R18 in the general formula (3) each independently represent a hydrogen atom, an alkyl group, an aryl group, a halogen atom, an alkoxy group, or an aryloxy group. R25, R27, R28 , and R29 in the general formula (4) each independently represent a hydrogen atom, an alkyl group, an aryl group, a halogen atom, an alkoxy group, or an aryloxy group, with the proviso that at least one of R25 and R29 represents a hydrogen atom. R35, R36, and R38 in the general formula (5) each independently represent a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, or an aryloxy group.
In the general formulae (3) to (5), the alkyl groups and aryl groups have the same meaning as in the case of R1 and R2 in the general formula (1); the halogen atom has the same meaning as in the case of R3 and R4 in the general formula (1); and the alkoxy groups and aryloxy groups have the same meaning as in the case of R5 to R9 in the general formula (1).
Among the diazonium salts represented by the general formula (2), a diazonium salt represented by the following general formula (6) is preferable. 
In the general formula (6), R21 and R22 each independently represent an alkyl group and Xxe2x88x92 represents an anion, and the alkyl group and the anion have the same meaning as in the case of R1, R2 , and Xxe2x88x92 in the general formula (1). It is preferable that at least one of R21 and R22 is a methyl group.
The diazonium salt represented by the following general formula (9) is also desirable as a diazonium salt compound that can be used in the magenta heat-sensitive recording layer. 
In the general formula (9), Ar represents an aryl group; and R11 and R12 each represent a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms. In the general formula (9), R11 and R12 may be the same or different. Xxe2x88x92 represents an acid anion.
Specific examples of the diazonium salts represented by the general formulae (1), (2), (6), (8) and (9), respectively, are given below. It should be noted, however, that the invention is not limited to these compounds. 
The diazonium salt that is represented by any one of the general formulae (1), (2), and (6) can be prepared by a conventionally known method. That is, the diazonium salt can be synthesized by the diazotization of a corresponding aniline in an acidic solvent by use of sodium nitrite, nitrosylsulfuric acid, isoamyl nitrite, etc.
The diazonium salt that is represented by any one of the general formulae (1), (2), and (6) may be in any of an oily state and a crystalline state. In view of ease in handling, an diazonium salt that is in a crystalline state at room temperature is preferable.
These diazonium salts may be used alone, in a combination of two or more, or in combination with a conventional diazonium salt.
The content of the diazonium salt in the light-sensitive heat-sensitive recording layer of a light-sensitive heat-sensitive recording material is preferably 0.02 to 5 g/m2, more preferably 0.1 to 4 g/m2, from the viewpoint of the density of the color to be formed.
It is also possible to stabilize the diazonium salt by the formation of a complex compound thereof by use of zinc chloride, cadmium chloride, tin chloride, or the like.
The diazonium salt that is represented by any one of the general formulae (1), (2), and (6) reacts with a coupler that will be described later and provides a color having a high density. On the other hand, since the diazonium salt can be rapidly decomposed due to its excellent photodecomposability in the wavelength range of 380 to 460 nm of a fluorescent lamp or the like and thus the fixation can be completed sufficiently even by light irradiation of a short time, the diazonium salt is very useful as a color-forming component for a photofixable light-sensitive heat-sensitive recording material.
Next, the coupler (i.e., coupling component) to be used in the magenta heat-sensitive recording layer is explained below.
The coupler may be any compound capable of coupling-reacting with a diazonium compound to form a dye in a basic environment and/or a neutral environment. All of so-called 4-equivalent couplers for silver halide photographic photosensitive materials can be used as the couplers in the magenta heat-sensitive recording layers. According to the desired hues of magenta, these couplers can be selected. Examples of the coupler include a so-called active methylene compound having a methylene group adjacent to a carbonyl group, a phenol derivative, and a naphthol derivative. Specific examples of the couplers include the conventionally known couplers exemplified as those for the yellow heat-sensitive recording layer. These couplers can be used in so far as these couplers meet the purpose of the invention.
Among the couplers listed above, in particular the compounds represented by the following general formula (7) or tautomers thereof are preferable.
The details of the couplers represented by the general formula (7) are given below. 
wherein E1 and E2 each independently represent an electron attractive group. E1 and E2 may join together to form a ring. L represents a substituent that can leave at the time of coupling with a diazo compound.
The electron attractive groups represented by E1 and E2 mean, respectively, a substituent whose Hammett substituent constant "sgr"p is positive. These substituents may be the same or different. Preferred examples of the substituents include acyl groups such as an acetyl group, a propionyl group, a pivaloyl group, a chloroacetyl group, a trichloroacetyl group, a trifluoroacetyl group, a 1-methylcyclopropylcarbonyl group, a 1-ethylcyclopropylcarbonyl group, a 1-benzylcyclopropylcarbonyl group, a benzoyl group, a 4-methoxybenzoyl group, and a thenoyl group; oxycarbonyl groups such as a methoxycarbonyl group, an ethoxycarbonyl group, a 2-methoxyethoxycarbonyl group, and a 4-methoxyphenoxycarbonyl group; carbamoyl groups such a carbamoyl group, an N,N-dimethylcarbamoyl group, an N,N-diethylcarbamoyl group, an N-phenylcarbamoyl group, an N-[2,4-bis(pentyloxy)phenyl]carbamoyl group, an N-[2,4-bis(octyloxy)phenyl]carbamoyl group, and a morpholinocarbonyl group; alkylsulfonyl or arylsulfonyl groups such as a methanesulfonyl group, a benzenesulfonyl group, and a toluenesulfonyl group; phosphono groups such as a diethylphosphono group; heterocyclic groups such as a benzoxazole-2-yl group, a benzothiazole-2-yl group, a 3,4-dihydroquinazoline-4-one-2-yl group, and a 3,4-dihydroquinazoline-4-sulfone-2-yl group; nitro group; imino group; and cyano group.
The electron attractive groups represented by E1 and E2 may join together to form a ring. The rings formed by E1 and E2 are preferably 5- to 6-membered carbocycles or heterocycles.
In the general formula (7), L represents a substituent that can leave at the time of coupling with a diazonium salt. It is preferable that the group represented by L is a halogen atom, an alkylthio group which may have a substituent, an arylthio group which may have a substituent, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, an arylsulfonyloxy group which may have a substituent, an acyloxy group which may have a substituent, a benzoyloxy group which may have a substituent, a dialkylaminocarbonyloxy group which may have a substituent, a diarylaminocarbonyloxy group which may have a substituent, an alkoxycarbonyloxy group which may have a substituent, an aryloxyarbonyloxy group which may have a substituent, an N-pyrazolyl group which may have a substituent, an N-imidazolyl group which may have a substituent, or an N-benzotriazolyl group which may have a substituent.
Specific examples of the couplers represented by the general formula (7) are given are given below, but it should be understood that the invention is not restricted to these examples. The tautomers of the following couplers are also suitable. 
The tautomer of the above-mentioned coupler means a coupler that can exist as an isomer of the above-mentioned coupler, and the structures of the two couplers can be changed easily into each other. The tautomers are also preferable as the couplers to be used in the invention.
In the magenta heat-sensitive recording layer, the total mol of the coupler(s) added is preferably 0.5 to 10 times, and more preferably 1 to 5 times as large as the mol of the diazonium salt added in the magenta heat-sensitive recording layer from the standpoint of the effects.
When the total mol of the coupler(s) added is less than 0.5 times as large as the mol of the diazonium salt added, sufficient color-formability may not be obtained. On the other hand, the total mol of the total coupler(s) added, which is more than 10 times, impairs color-formability because of the problem of heat efficiency and is not desirable in view of the thickness.
Basic Substances
The basic substances include an inorganic or organic basic substance and a compound which, when heated, releases an alkaline substance as a result of decomposition or the like. Typical examples include nitrogen-containing compounds such as organic ammonium salts, organic amines, amides, urea and thiourea and derivatives thereof, thiazoles, pyrroles, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, formamidines, and pyridines. Specific examples of these compounds include tricyclohexylamine, tribenzylamine, octadecylbenzylamine, stearylamine, allylurea, thiourea, methylthiourea, allylthiourea, ethylenethiourea, 2-benzylimidazole, 4-phenylimidazole, 2-phenyl-4-methylimidazole, 2-undecylimidazoline, 2,4,5-trifuryl-2-imidazoline, 1,2-diphenyl-4,4-dimethyl-2-imidazoline, 2-phenyl-2-imidazoline, 1,2,3-triphenylguanidine, 1,2-dicyclohexylguanidine, 1,2,3-tricyclohexylguanidine, guanidine trichloroacetate, N,Nxe2x80x2-dibenzylpiperazine, 4,4xe2x80x2-dithiomorpholine, morpholinium trichloroacetate, 2-aminobenzothiazole, 2-benzoylhydrazinobenzothiazole, etc. These organic bases may be used in combinations of two or more.
Sensitizers
As to the sensitizer, an organic compound, which has a low melting point and has properly an aromatic group and a polar group inside the molecule, is preferable. Examples of such organic compound include benzyl p-benzyloxybenzoate, xcex1-naphthyl benzyl ether, xcex2-naphthyl benzyl ether, phenyl xcex2-naphthoate, phenyl xcex1-hydroxy-xcex2-naphthoate, xcex2-naphthol-(p-chlorobenzyl) ether, 1,4-butandiol phenyl ether, 1,4-butandiol-p-methylphenyl ether, 1,4-butandiol-p-ethylphenyl ether, 1,4-butandiol-m-methylphenyl ether, 1-phenoxy-2-(p-tolyloxy)ethane, 1-phenoxy-2-(p-ethylphenoxy)ethane, 1-phenoxy-2-(p-chlorophenoxy)ethane, p-benzylbiphenyl, etc.
Microcapsules
In the invention, the method of using the diazo compound and/or diazonium salt, the coupler which reacts with the diazo compound or the like upon heating to form a color, the basic substance, and the sensitizer is not particularly limited. And, any of the following methods may be employed. That is, (1) a method in which these compounds are used as a dispersion of solid particles; (2) a method in which these compounds are used as a dispersion by emulsification; (3) a method in which these compounds are used as a polymer dispersion; (4) a method in which these compounds are used as a latex dispersion; and (5) a method in which these compounds are encapsulated in microcapsules. Among these methods, the method in which the compounds are encapsulated in microcapsules is preferable from the viewpoint of preservability. In particular, a method, in which the diazo compound and the diazonium salt are enclosed in microcapsules, is preferable.
As for the method of encapsulation in microcapsules, a conventionally known method of encapsulation in microcapsules can be employed. The method is as follows. Color-forming agents, additives, and a microcapsule wall precursor are dissolved in an organic solvent which is difficultly soluble or insoluble in water. The resulting solution is added into an aqueous solution of a water-soluble polymer; emulsified by means of a homogenizer or the like; and heated so that a wall film of a polymeric substance constituting a microcapsule wall film is formed in the oil/water interface.
Examples of the organic solvent include low-boiling auxiliary solvents such as acetic ester, methylene chloride, and cyclohexanone and/or phosphoric ester, phthalic ester, acrylic ester, methacrylic ester, other carboxylic acid esters, fatty acid amides, alkylated biphenyl, alkylated terphenyl, alkylated naphthalene, diaryl ethane, chlorinated paraffin, alcohols, phenols, ethers, monoolefins, and epoxies. Specific examples include high-boiling oils such as tricresyl phosphate, trioctyl phosphate, octyl diphenyl phosphate, tricyclohexyl phosphate, dibutyl phthalate, dioctyl phthalate, dilauryl phthalate, dicyclohexyl phthalate, butyl oleate, diethylene glycol benzoate, dioctyl sebacate, dibutyl sebacate, dioctyl adipate, trioctyl trimellitate, acetyltriethyl citrate, octyl maleate, dibutyl maleate, isoamylbiphenyl, chlorinated paraffin, diisopropylnaphthalene, 1,1xe2x80x2-ditolylethane, 2,4-di-t-amylphenol, N,N-dibutyl-2-butoxy-5-t-octylaniline, 2-ethylhexyl hydroxybenzoate, and polyethylene glycol. Among these high-boiling oils, alcohols, phosphoric esters, carboxylic acid esters, alkylated biphenyl, alkylated terphenyl, alkylated naphthalene, and diaryl ethane are preferable. Further, a carbonization inhibitor such as a hindered phenol or a hindered amine may be added to these high-boiling oils. In particular, an oil comprising an unsaturated fatty acid is preferable as the oil and examples thereof include an xcex1-methylstyrene dimer. Examples of the xcex1-methylstyrene dimer include xe2x80x9cMSD100xe2x80x9d (trade name, manufactured by Mitsui Toatsu Chemicals, Inc.)
A water-soluble polymer such as polyvinyl alcohol is used as the water-soluble polymer. In this case, a hydrophobic polymer emulsion or latex or the like can be used together with the water-soluble polymer. Examples of the water-soluble polymer include polyvinyl alcohol, silanol-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amino-modified polyvinyl alcohol, itaconic acid-modified polyvinyl alcohol, styrene/maleic anhydride copolymers, butadiene/maleic anhydride copolymers, ethylene/maleic anhydride copolymers, isobutylene/maleic anhydride copolymers, polyacrylamide, polystyrenesulfonic acid, polyvinyl pyrrolidone, ethylene/acrylic acid copolymers, and gelatin. Among these water-soluble polymers, carboxy-modified polyvinyl alcohol or gelatin is particularly preferable. Examples of the hydrophobic polymer emulsion or latex include styrene/butadiene copolymers, carboxy-modified styrene/butadiene copolymers, and acrylonitrile/butadiene copolymers. In this case, a conventionally known surfactant or the like may be added as necessary.
Specific examples of the polymeric material constituting a microcapsule wall film include a polyurethane resin, a polyurea resin, a polyamide resin, a polyester resin, a polycarbonate resin, an aminoaldehyde resin, a melamine resin, a polystyrene resin, a styrene/acrylate copolymer resin, a styrene/methacrylate copolymer resin, gelatin, and polyvinyl alcohol. Among these examples, a polyurethane/polyurea resin is particularly preferable as the wall-forming material.
The microcapsules having a wall film composed of a polyurethane/polyurea resin are prepared by the steps of blending a microcapsule wall precursor such as a polyvalent isocyanate into a core material to be encapsulated, dispersing the blend by emulsification into an aqueous solution of a water-soluble polymer such as polyvinyl alcohol or gelatin, and heating the resulting liquid so that a polymer forming reaction takes place in the interface of oil droplets.
Some specific examples of the polyvalent isocyanate compound are given below. For example, these are diisocyanates such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate, 3,3xe2x80x2-diphenylmethane-4,4xe2x80x2-diisocyanate, xylylene-1,4-diisocyanate, 4,4xe2x80x2-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, and cyclohexylene-1,4-diisocyanate; triisocyanates such as 4,4xe2x80x2,4xe2x80x3-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate; tetraisocyanates such as 4,4xe2x80x2-dimethylphenylmethane-2,2xe2x80x2, 5,5xe2x80x2-tetraisocyanate; and isocyanate prepolymers such as a hexamethylene diisocyanate/trimethylol propane adduct, a 2,4-tolylene diisocyanate/trimethylol propane adduct, a xylylene diisocyanate/trimethylol propane adduct, and a tolylene diisocyanate/hexanetriol adduct. If necessary, two or more kinds of the polyvalent isocyanate compounds can be used. Among these polyvalent isocyanate compounds, a compound having three or more isocyanate groups in the molecule is particularly preferable.
In the method of encapsulation, the oils listed for dispersion by emulsification can be used as the organic solvents for dissolving the color-forming agents, additives, and microcapsule wall precursors. The same applies to the water-soluble polymers.
The particle diameter of the microcapsule is preferably 0.1 to 1.0 xcexcm and more preferably 0.2 to 0.7 xcexcm.
Recording Methods
According to the heat-sensitive recording material of the invention, a multicolor heat-sensitive recording material is formed by the lamination of at least three layers of heat-sensitive layers comprising different diazonium salt compounds whose light-sensitive wavelengths differ from one another and couplers which reacts, respectively, with the diazonium salt compounds upon heating to form different colors.
For example, the heat-sensitive recording material comprises a support having disposed thereon a first heat-sensitive recording layer (yellow heat-sensitive recording layer) containing a diazo compound or the like whose maximum absorption wavelength is 350 nm or less and a coupler which reacts with the diazo compound or the like to develop a color upon heating, a second heat-sensitive recording layer (cyan heat-sensitive recording layer) containing a diazonium salt compound whose maximum absorption wavelength is 370xc2x130 nm and a coupler which reacts with the diazo compound or the like to develop a color upon heating, and a third heat-sensitive recording layer (magenta heat-sensitive recording layer) containing a diazo compound or the like whose maximum absorption wavelength is 430xc2x130 nm and a coupler which reacts with the diazo compound or the like to develop a color upon heating.
The method of recording in this multicolor heat-sensitive recording material is as follows. First, the third heat-sensitive recording layer (magenta heat-sensitive recording layer) is heated so that a color is formed by the reaction between the diazo compound or the like and the coupler contained in the layer. Next, the third heat-sensitive recording layer is irradiated with light having a wavelength of 430xc2x130 nm so that the diazo compound or the like remaining unreacted in the third heat-sensitive recording layer is decomposed. After that, suffcient heat to cause the second heat-sensitive recording layer (cyan heat-sensitive recording layer) to develop a color is applied to the second heat-sensitive recording layer and a color is formed by the reaction between the diazo compound or the like and the coupler contained in the layer. When the heat is applied, although the third heat-sensitive recording layer is also heated strongly, the third heat-sensitive recording layer does not develop any color because the diazo compound or the like is already decomposed to an extent that its color-forming capability is lost. Further, the second heat-sensitive recording layer is irradiated with light having a wavelength of 370xc2x130 nm so that the diazo compound or the like remaining unreacted in the second heat-sensitive recording layer is decomposed. Finally, sufficient heat to cause the first heat-sensitive recording layer to develop a color is applied to the first heat-sensitive recording layer. When the heat is applied, although the third and second heat-sensitive recording layers are also heated strongly, these heat-sensitive recording layers do not develop any color because the diazo compounds or the like contained in the third and second heat-sensitive recording layers are already decomposed to an extent that their color-forming capability is lost.
The light sources to be used for the photodecomposition (photo-fixation) of the diazo compound or the like include various kinds of fluorescent lamps, xenon lamps, mercury lamps, etc. For the purpose of efficient fixation, it is preferable that the light emission spectra of these light sources are approximately equal to the absorption spectra of the diazonium salts in the heat-sensitive recording material.
In particular, it is most preferable to use a light source that emits light whose central wavelength is 340 to 460 nm in the invention.
The heat-sensitive recording material can also be used as a light-writable heat development type heat-sensitive recording material in which image-wise writing is made by light and images are produced by heat development. In this case, the steps of printing and imaging are carried out by a light source such as a laser in place of the heating device described above.
Antioxidants
In the invention, in order to further improve the lightfastness, conventionally known antioxidants described in the following publications can be used. Examples of the antioxidants include those described in, for example, EP No. 310551A, German Patent Application Laid-Open (OLS) No. 3435443, EP No. 310552A, JP-A No. 3-121449, EP No. 459416A, JP-A Nos. 2-262654, 2-71262, and 63-163351, U.S. Pat. No. 4,814,262, JP-A Nos. 54-48535, 5-61166, and 5-119449, U.S. Pat. No. 4,980,275, JP-A Nos . 63-113536 and 62-262047, EP Nos. 223739A, 309402A, 309401A, etc. Specific examples include the following; 
It is also effective to use additives conventionally known as those for use in heat-sensitive recording materials and pressure-sensitive recording materials. Some examples of these antioxidants include the compounds described in JP-A Nos. 60-125470, 60-125471, 60-125472, 60-287485, 60-287486, 60-287487, 62-146680, 60-287488, 62-282885, 63-89877, 63-88380, 63-088381, 01-239282, 04-291685, 04-291684, 05-188687, 05-188686, 05-110490, 05-1108437, 05-170361, 63-203372, 63-224989, 63-267594, 63-182484, 60-107384, 60-107383, 61-160287, 61-185483, 61-211079, 63-251282, and 63-051174, Japanese Patent Application Publication (JP-B) Nos. 48-043294 and 48-033212, etc.
Specific examples of the antioxidants include 6-ethoxy-1-phenyl-2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethoxy-1-phenyl-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline, 6-ethoxy-1-octyl-2,2,4-trimethyl-1,2,3,4-tetrahydroquinoline, nickel cyclohexanoate, 2,2-bis-4-hydroxyphenylpropane, 1,1-bis-4-hydroxyphenyl-2-ethylhexane, 2-methyl-4-methoxy-diphenylamine, 1-methyl-2-phenylindole, and the compounds listed below. 
These antioxidants can be incorporated in a heat-sensitive recording layer or an intermediate layer, a light transmittance-adjusting layer, and a protective layer. In the case where these antioxidants are used in a combination, the examples of the combination include a combination of the specific example (Q-7), (Q-45), (Q-46), or (Q-10) and the compound (Q-13).